The present invention relates to a pneumatic tire, and more particularly to a bead structure suitable for radial ply tires for a passenger car, which can reduce the occurrence of carcass ply turned up edge looseness and can suppress the growth of the occurred looseness to improve the durability of the tire.
In general, as shown in FIG. 3, a radial tire has a carcass ply (b) turned up around bead cores (a) from the axially inside to the outside thereof to be secured thereto, a bead filler ply (c) disposed between the bead core and the carcass to prevent the carcass cords from abrasion, and a chafer (d) disposed along the bead profile to reinforce the bottom of the bead, and on the axially outside of the bead core (a). The bead filler ply (c) and the chafer (d) are terminated radially inside the edge of the carcass ply turned up portion (e), that is, the outer edge of the turned up portion of the carcass ply is projected from the edges of the the bead filler and the chafer and extended over the outer edge of the rim flange (f).
The turned up portion (e) is therefore, apt to be subjected to a compressive stress when the sidewall is deformed as shown in FIG. 4.
More, when subjected to a large deformation, the carcass ply turned up portion is bent abruptly over the rim flange, and the compressive stress is concentrated on that portion, and finally the carcass ply is broken by the cord fatigue due to the repeated large stress, which induces a further concentration of the compressive stress. Such concentration decreases not only the carcass strength but also the rubber strength.
Thus, bead failure generally occurs near the edge of the rim flange (f).
Therefore, it has been proposed to dispose axially outward of the carcass ply turned up portion an additional reinforcing cord layer to cover the edge of the carcass ply turned up portion.
The ply separation at the carcass ply turned up edge is reduced by the added cord layer, but ply separation at the edge of the added cord layer still remains unreduced.
Such cord layer has further problems such as an increase in the thickness of the sidewall and bead, an increase in the tire weight, an increase in the heat generation therefrom and the like.
It is therefore, an object of the present invention to provide a pneumatic tire and rim combination for reducing ply separation at the edge of the carcass ply turned up portion, and suppressing the growth of ply separation if caused without adding any reinforcing cord layer.